166 research outputs found
Pengaruh Faktor dan Mekanisme Pengerasan Regangan pada Baja Hadfield
No full textAbstract. Hadfield steel has good toughness, ductility, impact resistance, wear resistance and has excellent work hardening. It has a carbon content of 1-1.4% and manganese 11-14% by weight, a ratio of approximately 1:10. The potential for increasing its strength against strain hardening can be seen from the wide range of plastic strength, 379 MPa yield strength and 965 MPa tensile strength. The hardening of Hadfield steel strain depends on the type loading which affect the dislocation slip mechanism, twinning deformation, and the interaction between slip and twinning. The study of high strain rates in Hadfield steel is quite interesting and still relevant to date, although there have been many papers published. Hadfield cast steel which has a relatively low hardness, can be increased its hardness by treatment and high work hardening (high strain rate). There are factors that influence the hardness of Hadfield steel include alloying, solid solution process and high work hardening. Nitrogen as austenite stabilizer is important for work hardening, chromium and vanadium are added to increase hardness because it will form carbides, and aluminum is added to increase wear resistance. High strain rate deformation is applied to provide improved strength because of propensity of twinning mechanism is likely to occur. Optimum strain hardening by twinning mechanism can only be achieved at critical impact energy. Explosive hardening generates small deformations but provides significant changes in mechanical properties.Abstrak. Baja Hadfield memiliki sifat ketangguhan, keuletan, ketahanan impak, ketahanan terhadap aus dan memiliki work hardening yang sangat baik. Memiliki kandungan unsur karbon 1-1,4% dan mangan 11-14% berat, rasio kurang lebih 1:10. Potensi peningkatan kekuatan terhadap pengerasan regangan, dapat dilihat dari rentang kekuatan plastis yang lebar, kekuatan luluh 379 MPa dan kekuatan tarik 965 MPa. Pengerasan regangan baja Hadfield tergantung kepada proses pembebanan melalui mekanisme slip dislokasi, deformasi twinning, serta interaksi antara slip dan twinning. Kajian tentang high strain rate pada baja Hadfield menjadi topik yang cukup menarik dan relevan, meskipun telah banyak publikasi yang dihasilkan. Baja Hadfield yang memiliki kekerasan relatif rendah, mampu ditingkatkan nilai kekerasannya melalui rekayasa perlakuan panas dan deformasi plastis secara cepat. Beberapa faktor yang mempengaruhi kekerasan baja Hadfield antara lain bahan paduan, perlakuan panas dan proses pengerasan regangan yang diberikan. Nitrogen sebagai penstabil austenit penting untuk pengerjaan dingin, kromium dan vanadium ditambahkan untuk meningkatkan kekerasan karena akan membentuk karbida, dan aluminum ditambahkan untuk meningkatkan ketahanan aus. Deformasi kecepatan regangan tinggi pada Hadfield memberikan peningkatan kekuatan lebih baik karena mekanisme twinning lebih dominan. Pengerasan regangan optimum oleh mekanisme twinning hanya dapat dicapai pada energi impak kritikal. Explosive hardening menghasilkan deformasi yang relatif kecil tetapi memberikan perubahan sifat mekanik yang signifikan
Pengaruh Media Pendingin Pada Proses Hardening Terhadap Strukturmikro Baja Mangan Hadfield AISI 3401 PT Semen Gresik
No full textBaja Mangan Hadfield termasuk dalam kategori baja mangan austenitic dengan kandungan Mn (mangan) yang tinggi, antara 12-14% Mn dan 0.8-1.25% C. Baja mangan hadfield memiliki kekerasan, kekuatan, ketangguhan, serta ketahanan terhadap aus yang tinggi. Proses hardening diberikan dengan melakukan pendinginan yang relatif cepat dengan menggunakan media pendingin air, oli, polivinylalcohol 10%, dan polyvinylalcohol 40% bertujuan untuk mendapatkan nilai kekerasan yang lebih tinggi yakni dengan pendinginan air 275VHN sedangkan tanpa perlakuan 206VHN. Viskositas dari media pendingin yang berbeda-beda berpengaruh terhadap laju pendinginan pada baja mangan hadifield.. Jenis media pendingin yang bervariasi mempengaruhi perubahan austenit menjadi martensit. Strukturmikro yang terbentuk pada baja mangan hadfield yang mengalami proses hardening tampak butir-butir kristal yang seluruhnya martensit, sedangkan pada baja mangan hadfield yang tanpa mendapatkan perlakuan tampak karbida mangan lamellar dengan matriks austenit.</p
Pengaruh Variasi Media Pendingin Proses Quenching Terhadap Mikrostruktur dan Sifat Mekanik Baja Hadfield
No full textManganese steel contains 1,2% C and 12% Mn generally recognized as Hadfield steel. Based on the high composition of C and Mn elements, the main structure of this steel is dominated by an austenite matrix that surrounded the carbide phase on the grain boundary. This structure is usually brittle which leads to improper high-loading conditions. To overcome this problem, the experimental method was carried out by heating Hadfield steel to a temperature of 1000 oC, then followed by a quenching process using cooling media variations namely water and salt bath (20 wt.% NaCl solution). These cooling media variations aim to determine the level of carbide formation which affects the microstructure and mechanical properties. From the test results, it was obtained that Hadfield steel with salt bath (20 wt.% NaCl) quenching variation has significant microstructure transformation which affects enhancement of the value of tensile and yield strength (809,5 and 542,4 MPa), hardness (238 HV), ductility and toughness.Baja mangan yang mengandung 1,2% C dan 12% Mn dikenal secara umum sebagai baja Hadfield. Berdasarkan tingginya kandungan unsur C dan Mn, struktur utama baja ini didominasi oleh matriks austenit yang dikelilingi fasa karbida pada batas butirnya. Struktur tersebut biasanya rapuh dan cenderung tidak layak untuk penggunaan dalam kondisi pembebanan tinggi. Untuk mengatasi permasalahan tersebut, metode eksperimen dilakukan dengan cara memanaskan baja Hadfield hingga temperatur 1000 °C, kemudian dilanjutkan dengan proses quenching menggunakan variasi media pendingin yaitu air dan air garam 20 wt.% NaCl. Pemilihan variasi media pendingin ini bertujuan untuk mengetahui tingkat pembentukan fasa karbida dan pengaruhnya terhadap mikrostruktur dan sifat mekaniknya. Dari hasil pengujian didapatkan bahwa baja Hadfield dengan variasi quenching air garam 20 wt.% NaCl memiliki transformasi mikrostruktur yang signifikan sehingga berefek pada peningkatan nilai kekuatan tarik dan luluh (809,5 dan 542,4 MPa), kekerasan (238 HV), keuletan dan ketangguhannya
Pengaruh Media Pendingin Pada Proses Hardening Terhadap Strukturmikro Baja Mangan Hadfield AISI 3401 PT Semen Gresik
No full textBaja Mangan Hadfield termasuk dalam kategori baja mangan austenitic dengan kandungan Mn (mangan) yang tinggi, antara 12-14% Mn dan 0.8-1.25% C. Baja mangan hadfield memiliki kekerasan, kekuatan, ketangguhan, serta ketahanan terhadap aus yang tinggi. Proses hardening diberikan dengan melakukan pendinginan yang relatif cepat dengan menggunakan media pendingin air, oli, polivinylalcohol 10%, dan polyvinylalcohol 40% bertujuan untuk mendapatkan nilai kekerasan yang lebih tinggi yakni dengan pendinginan air 275VHN sedangkan tanpa perlakuan 206VHN. Viskositas dari media pendingin yang berbeda-beda berpengaruh terhadap laju pendinginan pada baja mangan hadifield.. Jenis media pendingin yang bervariasi mempengaruhi perubahan austenit menjadi martensit. Strukturmikro yang terbentuk pada baja mangan hadfield yang mengalami proses hardening tampak butir-butir kristal yang seluruhnya martensit, sedangkan pada baja mangan hadfield yang tanpa mendapatkan perlakuan tampak karbida mangan lamellar dengan matriks austenit
Motivating learning / Jill Hadfield and Zoltan Dornyei.
No full textIncludes bibliographical references.viii, 307 p.
Analisis Pengaruh Media Pendinginan pada Proses Perlakuan Panas Baja Hadfield terhadap Struktur Mikro dan Kekerasan
No full textHadfield steel is steel with a content of 10-14% Mn and 1.0-1.4% C. Casting Hadfield steel contains carbide (Fe, Mn)3C at grain boundaries which can reduce strength so that it is given heat treatment so that the carbide dissolves. Rapid cooling of Hadfield steel in aqueous media prevents the formation of carbides at the grain boundaries. However, the cooling medium affects the cooling rate which changes the microstructure and mechanical properties of Hadfield steel. The purpose of this study was to analyze the effect of the cooling media water, ice water and oil in the heat treatment process on the microstructure and hardness of Hadfield steel. The heat treatment was initiated using a pre-austenizing temperature of 700℃ with a holding time of 60 minutes, followed by austenizing temperatures of 1150℃ and 1200℃ with a holding time of 30 minutes. After that, rapid cooling using the media of water, ice water and oil is then carried out mounting, grinding, polishing and etching. Testing the microstructure using an optical microscope and SEM while the Vickers hardness test. The results showed that heat treatment at 1150℃ followed by water+ice cooling produced a higher amount of carbide compared to water and oil, whereas at 1200℃ heat treatment with water+ice cooling produced a lower amount of carbide compared to water and oil. The highest hardness value was 185.1 HV at 1150℃ heat treatment followed by water+ice cooling, while the lowest hardness value was 174.3 HV produced by 1150℃ heat treatment with oil cooling. The highest hardness value of 187.6 HV was produced by heat treatment at 1200℃ followed by water cooling, while water+ice cooling produced the lowest hardness value of 168.2 HV
PENGARUH QUENCH DAN TEMPERING TERHADAP SIFAT FISIS DAN MEKANIS BAJA HADFIELD HASIL PENGECORAN PT. BAJA KURNIA
No full textTelah dilakukan penelitian untuk mengetahui prosentase unsur utama
penyusun komposisi kimia, fasa struktur mikro, harga kekerasan dan
keausan (wear resistant) pada baja manganese steel ( hadfield ) dengan
variasi spesimen : raw material, quenching 1200 °C, te mpering after
quenching 600 °C dengan waktu tahan 15 dan 30 meni t.
Bahan yang digunakan dalam penelitian ini adalah baja mangan
ScMnH11 standard JIS yang diproduksi PT. Baja Kurnia di Batur Ceper
Klaten. Pemberian laku panas di dalam tungku ( furnace) 1200 °C selama 30
menit kemudian di quenching dengan air dingin dan dilanjutkan tempering
pada suhu 600 °C selama 15 dan 30 menit. Pengujian yan g dilakukan adalah
uji komposisi kimia, uji struktur mikro, uji kekerasan dan uji keausan.
Dari hasil pengujian komposisi kimia pada spesimen Baja mangan
ScMnH11 didapatkan unsur penyusun utama adalah besi (Fe) = 82,0 %;
karbon (C) = 1,22 % dan mangan (Mn) = 13,4 %. Dari hasil pengamatan
struktur mikro pada spesimen raw material dan spesimen quenching
didapatkan fasa ferit, cementit (Fe 3 C), austenit dan lapisan tipis martensit,
spesimen tempering after quenching 600 °C 15 dan 30 menit didapatkan
fasa perlit, Fe3C serta austenit. Dari pengujian kekerasan didapatkan harga
kekerasan rata-rata teringgi pada spesimen Quenching 1200 °C sebesar
243,83 VHN dan berturut-turut menuju posisi terendah, yaitu raw material
sebesar 242,03 VHN spesimen tempering after quenching 600 °C selama
30 menit sebesar 228,80 VHN, dan paling rendah spesimen tempering after
quenching 600 °C,15 menit sebesar 191,37 VHN. Dari hasil pengujian
keausan didapatkan harga keausan rata-rata dari yang tertinggi adalah
spesimen tempering after quenching 600 °C selama 15 me nit sebesar
3,221´ 10 -7mm²/kg, spesimen tempering after quenching 600 °C selam a 30
menit sebesar 2,693´ 10 -7mm²/kg kemudian raw material sebesar 1,947 ´ 10
-7mm²/kg dengan nilai keausan terendah adalah spesimen quenching 1200
°C sebesar 1,906 ´ 10 -7mm²/kg
THE USE OF PICTURE SERIES TO IMPROVE STUDENTS’ ABILITY IN WRITING RECOUNT TEXTS (A Classroom Action Research on the Eight Grade of SMP N 3 Kartasura in 2009/2010 Academic Year)
No full textWriting is as a means of communication. Writing involves transferring a
message from our thoughts using language in the written form and it is a
communicative competence. According to Brown (1994: 227), communicative
competence is relative, not absolute, and depends on the cooperation of all the
participants. Communicative competence enables one to convey and interpret
messages and to negotiate meanings interpersonally within specific context. In
addition, Canale and Swain (in Brown, 1994: 227) state that communicative
competence consists of grammatical competence, discourse competence,
sociolinguistic competence, and strategic competence. The grammatical
competence and discourse competence reflect the use of linguistic system itself. The
sociolinguistic competence and strategic competence reflect the functional aspects
of communication. By acquiring communicative competence, the students are
expected to have knowledge of grammar and vocabulary of the language; to have
knowledge of rules of writing and to be able to apply it in real communication
appropriately.
Writing is a productive skill. It is very useful for students because it can convey
their message through their minds in the written form. It is placed on the last stage
among the four skills. Writing is the production of the written word in the form of
text and it must be read and comprehended in order to communicate to take place.
In other words, in writing, a writer communicates his/her ideas by considering a
known or unknown reader who will get their ideas and their meanings in the form
of correct written text. To write well, people must have good writing capabilities
too. Moreover, someone who wants to write essay or story must know in writing
process and the aspects of writing skills. The people must be able to organize the
idea, to construct sentences, to use the spelling and punctuation well. Besides, they
must be able to arrange their writings into cohesive and coherent paragraphs and
texts.
According to Scott and Ytreberg (1998: 69), writing is a good thing. Even if
there are difficulties in writing in the foreign language, it is still useful, essential,
integral and enjoyable part of the foreign language lesson. Writing can add another
physical dimension to the learning process; it lets pupils express their personalities;
it helps to consolidate learning in the other skill areas; it allows for conscious
development of language; and it is valuable in itself.
Writing is not a natural skill because one can’t acquire this ability automatically
and easily. Writing skill differs from others skill like speaking and listening. The
two other skills can be gained through natural processes. Since one was born, he has
got considerable experiences of listening and speaking. In writing, he must
recognize and understand new symbols. It is in schools that he gets knowledge of
new symbols in the written form when beginning to understand the significance of
letter on paper. Writing is therefore a sophisticated skill combining a numbers of
different elements that must be grammatically connected. Writing is considered the most difficult to be learned and mastered because it
involves some language components (spelling, language use, vocabulary, and
punctuation). Writing requires the rules of English grammar and mechanics such as
the correct use of verbs and pronouns, as well as commas and other marks of
punctuation and it also involves many aspects such as paragraph development,
organization of content and it demands standard form of grammar, syntax, and
vocabulary. In writing, the relationships between sentences operate at several levels.
There needs to be thematic unity; there need also to be a logical progression, often
made clear by the use of conjunctions which express on the surface an underlying
logic in the propositions of the text; there needs also to be grammatical linkage
between sentences (Harris, 1993: 6).
According to Hadfield (2004: v), there are some difficulties related to the
writing. Firstly, there is psychological difficulty in which the writer has to decide
what the information the reader needs and how best to express this. Secondly, there
is linguistic difficulty in that the language used in written language is different from
that used in speech. Thirdly, there is cognitive difficulty in which that the students
have to organize their thought on paper. That is why writing is regarded as the most
difficult language skill to learn for a language learner.
The students of class VIII-E SMP N 3 Kartasura also faced some problems
above. Based on the observation conducted, it was found that the students’ ability in
writing recount texts was still far from what was expected. From the result of the
students’ writing, the average score of the students was 52.65. This score was
computed from the average score of the element of writing. The first element depends on the content that was 16.66. The average score of organization was 10.76
and followed by the average of vocabulary, 10.51. The last two elements of writing
were grammar and mechanic which had the average score 11.13 and 3.57. From the
writing score, there were only 3 students who got writing score above 67.5. It
means they could fulfil the passing grade of writing skill in English lesson. While
the others 32 students got score under 67.5. It means that they still failed to write
English well. The scores of the students showed that the worst element of writing is
on content. Then, it was followed by grammar, vocabulary, organization, and
mechanic. Most of their writing consists of ungrammatical sentences; their ideas
moved away from focus and sometimes did not have any supporting details. They
also had incorrect spelling and punctuation errors. It could be concluded that they
still could not write English well.
These evidences were also supported by the result of interview. The interview
was conducted to know the students’ perception toward writing skill. When the
students were asked about writing, most of them reacted that writing is difficult. It
could be seen from quotations of the following result of interview:
- “Nulisnya sulit, mas. Tulisannya jelek og.” (A.3)
- “Nulisnya itu dalam terjemahannya bahasa Indonesia ke bahasa Inggris
gitu. Kosakatanya juga lumayan susah.” (A.7)
- “Ya, pokoknya menulis itu sulit. Menulis itu agak-agak gimana gitu.”
(A.18)
- “Kosakatanya belum terlalu bisa. Pengembangan paragrafnya sulit” (A.29)
- “Gak bisa nulis og. Kosakatanya kurang.” (A.30)
It means that students still regarded writing as a difficult skill. Most of them found
difficulties in developing paragraph and finding appropriate vocabulary. Some of them did not know the correct spelling of some certain words. It means that they did
not revise what they had written.
The interview was also conducted to the teacher in order to know the condition
of the students of class VIII-E. The questions of interview were related to the
students’ writing ability, the difficulties that the students’ faced in writing, and the
teaching writing in class. The teacher said that the students of VIII-E SMP N 3
Kartasura have low ability in writing. As stated by the English teacher of class VIIIE:
“Writing skill mereka belum terlalu bagus karena terkendala dengan
vocabulary yang mereka punya. Mereka juga kurang begitu aktif dalam menulis
karena lack of vocabularies tadi.”
She also stated that the students got difficulties in developing paragraph, using
correct tense, and finding appropriate vocabulary which could be seen from the
result of interview as follows:
“Siswa pasif karena terkendala dalam mengembangkan kalimat. Mereka juga
masih lack of vocabularies atau kurang dalam kosakata. Mereka juga masih
lemah dalam comprehension begitu pula dengan past verb mereka juga masih
sangat lemah.”
The teacher seldom taught writing to the students through writing process. She
just explained the patterns and gave the example of the text, and then she asked
the students to write a certain topic without any guidance, as what she said in the
interview:
“Setelah saya ajarkan mereka tentang ciri-ciri dan contoh dari teks tersebut
kemudian saya suruh mereka untuk menulis paragraph berdasarkan teks yang
dimaksud dan saya juga jarang menyuruh mereka untuk menulis teks jadi
mereka juga agak kurang dalam menulis.” From the result of interview, it could be concluded that the students still have
low ability in writing. They faced problems in writing, especially in making
correct grammatical sentences, developing paragraph and finding appropriate
vocabulary. In addition, the teacher seldom taught writing to the students through
writing process which only gave the students to write in a certain topic without
any guidance. She only demanded the product of students’ writing.
The result of questionnaire also showed that 73.5 % of students felt that
writing is difficult. They did not like when the teacher asked them to write. Most
of them, 61.8 %, felt that the time given for writing is not enough. 55.9 % students
got difficulties in starting to write and 52.9 % seldom paid attention to choose
appropriate vocabulary even 20.6 % did not do that. 52.9 % students did not
arrange the outline or draft before writing.
From the preliminary observation then, the researcher concluded that there
were two main causes: from teacher and student. Firstly, the teacher did not apply
writing process in teaching writing. She just explained the characteristics and the
examples of the texts. Then, she only demanded the students’ writing product and
she only gave fewer portions for writing whereas writing is a complex activity.
The teacher just demanded the product of the students’ writing that must fulfil the
written language rules. Moreover, she did not give enough attention to teach
students how to write in English correctly. Writing class generally ignored the
writing process. The teacher asked the students to write in a certain topic. The
time given by the teacher was limited. The teacher did not consider that writing is
a complex activity in which it needs more time for revising the content, grammar and conducting consultation. Secondly, the students still did not master on writing
skill. Their ideas were not coherent. They sometimes lost their ideas and stuck.
So, they could not continue their writing. They did not also use tense in the right
context, because they were still confused to use tense correctly. They were lack of
vocabulary and their understanding of mechanic was low. They seldom read their
writing after they finished writing. That was why, their writing were not coherent.
They also thought that time for writing was limited. Because of these they got
difficulties in writing and the result of their writing were still far from what were
expected.
Based on the evidences above, the writer conducted a classroom action
research in order to improve the students' writing ability. The classroom action
research focused on the improving students’ writing ability especially in the form
of recount text. This was done for the reason that this kind of writing form was
suggested in the syllabus used in SMP that is KTSP. Usually in the writing class,
the teacher did not use a media to improve students’ writing ability yet. The
teacher only used handbook and students worksheet. In this research, the
researcher used picture series to improve students writing ability, especially in
writing recount text.
Picture in writing is one way to solve the problems in writing. Picture is
categorized as one of aids in language teaching. Visual aids are a situation where
the learner can see what is named by the word to be learned (Allen, 1983: 33).
Pictures are not just as aspect of method but through their representation of places,
objects, and people they are essential part of the overall experiences we must help our students to cope with (Wright, 1997: 2). In addition, he mentions that pictures
can be used by teacher and students whatever emphasis of the syllabus they are
following. Furthermore, he states pictures make particularly powerful contribution
to both the content and the process of language learning.
Using picture series in writing recount texts has many advantages. Raimes
(1983: 36) says that a picture sequence, such as comic strip, provides the subject
matter for writing narrative and for speculating about the story beyond the
pictures in the strip. A set of parallel picture – pictures that show a similar scene
or tell a similar story – provides material that offers guidance on vocabulary,
sentence structure, and organization yet lets the students write about new subject
matter. On the other hand, picture sequences in which there is ambiguity and the
opportunity for widely divergent interpretations are an excellent basis for
stimulating individual response and a variety of written outcomes. Besides, the
students usually have other perceptions and interpretations to the provided picture.
The students just want to see and focus to the one object from the provided
picture.
In this study, the writer tries to apply picture series during the writing process
because hopefully it can give students an interest and motivation in learning. By
providing it, the students will not be bored again to the writing and they can
develop and share their ideas in written form. It also makes a sense of the context
of a language for the students since writing needs more vocabularies that must be
mastered by the students. It also has a specific point or stimulus to the students in
process writing where it can also express their ideas and it can develop the content of writing. It can lead students to have new experience of real writing activity and
will give them understanding that writing is a means of communication. It also
gives students enough time to write since writing is a process of expressing ideas
in written form. It will provide information whether the students are already
successful in the running cycle or not
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