资源目录
压缩包内文档预览：
编号：139457076
类型：共享资源
大小：10.63MB
格式：ZIP
上传时间：2021-08-02
上传人：qq77****057
认证信息
个人认证
李**（实名认证）
江苏
IP属地：江苏
25
积分
- 关 键 词：
-
基于
三维
手机
模具设计
- 资源描述：
-
基于三维的手机后盖模具设计,基于,三维,手机,模具设计
- 内容简介：
-
STEELPLAIN CARBON STEELAny steel-making process is capable of producing a product that has 0.05% or less carbon 。With this small amount of carbon，the properties approach those of pure iron with maximum ductility and minimum strength。Maximum ductility is desirable front the standpoint of ease in deformation processing and service use。Minimum strength is desirable for deformation processing。However，higher strengths than that obtainable with this low carbon are desirable from the standpoint of product design。The most practical means of increasing the strength is by the addition or retention of some carbon。However，it should be fully understood that any increase of strength over that of pure iron can be obtained only at the expense of some loss of ductility，and the final choice is always a compromise of some degree。Because of the difficulty of composition control or the additional operation of increasing carbon content，the cost of higher carbon，higher strength steel is greater than that of low carbon。Plain Carbon Steels Most Used。Because of their low cost，the majority of steels used are plain carbon steels。These consist of iron combined with carbon concentrated in three ranges classed as low carbon，medium carbon，and high carbon。With the exception of manganese used to control sulphur，other elements are present only in small enough quantities to be considered as impurities，though in some cases they may have minor effect on properties of the material。Low Carbon。 Steels with approximately 6 to 25 point of carbon（0.06%0.25%）are rated as low carbon steels and are rarely hardened by heat treatment because the low carbon content permits so little formation of hard martensite that the process is relatively ineffective。Enormous tonnages of these low carbon steels are processed in such structural shapes as sheet，strip，rod，plate，pipe，and wire。A large portion of the material is cold worked in its final processing to improve its hardness，strength，and surface-finish qualities。The grades containing 20 points or less of carbon are susceptible to considerable plastic flow and are frequently used as deep-drawn products or may be used as a ductile core for casehardened material。The low plain carbon steels are readily brazed，welded，and forged。Medium Carbon。The medium carbon steels（0.25%0.5%）contain sufficient carbon that they may be heat treated for desirable strength，hardness，machinability，or other properties。The hardness of plain carbon steels in this range cannot be increased sufficiently for the material to server satisfactorily as cutting tools，but the load-carrying capacity of steels can be raised considerably，while still retaining sufficient ductility for good toughness。The majority of the steel is furnished in the hot-rolled condition and is often machine for final finishing。It can be welded，but is more difficult to join by this method than the carbon steel because of structural changes caused by welding heat in localize areas。High Carbon。 High carbon steel contains from 50 to 160 points of carbon（0.5%1.6%）。This group of steel is classed as tool and die steel，in which hardness is the principal property desired。Because of the fast reaction time and resulting low hardenability，plan carbon steels nearly always must be water quenched。Even with this drastic treatment and its associated danger of distortion or cracking，it is seldom possible to develop fully hardened structure in material more than about 1 inch in thickness。In practice the ductility of heat-treat-hardened plain carbon steel is low compared to that of alloy steels with the same strength，but even so，carbon steel is frequently used because of its lower cost。ALLOY STEELSAlthough plain carbon steels work well for many uses and are the cheapest steels and therefore the most used，they cannot completely fulfil the requirements for some work。Individual or groups of properties can be improved by addition of various elements in the form of alloys。Even plain carbon steels are alloys of at least iron，carbon，and manganese，but the term alloy steel refers to steels containing elements other than these in controlled quantities greater than impurity concentration or，in the case of manganese，greater than 1.5%。Alloys Affect Hardenability。Interest in hardenability is indirect。Hardenability is usually thought of most in connection with depth-hardening ability in a full hardening operation。However，with the isothermal transformation curves shifted to the right，the properties of a material can be materially changed even when not fully hardened。After hot-rolling or forging operations，the material usually air cools。Any alloy generally shifts the transformation curves to the right，which with air cooling results in finer pearlite than would be formed in a plain carbon steel。This finer pearlite has higher hardness and strength，which has an effect on machinability and may lower ductility。Weldability。 The generally had influence of alloys on weldability is a further reflection of the influence on hardenability。With alloys present during the rapid cooling taking place in the welding on area，hard，nonductile structures are formed in the steel and frequently lead to cracking and distortion。Grain Size and Toughness。 Nickel in particular has a very beneficial effect by retarding grain growth in the austenite range。As with hardenability，it is the secondary effect of grain refinement that are noted in properties。A finer grain structure may actually have less hardenability，but it has its most pronounced effect on toughness；for two steels with equivalent hardness and strength，the one with finer grain will have better ductility，which is reflected in the chart as improved toughness。This improved toughness，however，may be detrimental to machinability。Corrosion Resistance。 Most pure metals have relatively good corrosion resistance，which is generally lowered by impurities or small amounts of intentional alloys。In steel，carbon in particular lowers the corrosion resistance very seriously。In small percentages，copper and phosphorus are beneficial in reducing corrosion。Nickel becomes effective in percentages of about 5%，and chromium is extremely in percentages greater than 10%，which leads to a separate class of alloy steels called stainless steels。Many tool steels，while not designed for the purpose，are in effect stainless steels because of the high percentage of chromium present。LOW ALLOY STRUCTURAL STEELS Certain low alloy steels sold under various trade names have been developed to provide a low cost structural material with higher yield strength than plain carbon steel。The addition of small amounts of some alloying element can raise the yield strength of hot-rolled sections without heat treatment to 30%40% greater than that of plain carbon steels。Designing to higher working stresses may reduce the required section size by 25%30% at an increased cost of 15%50%，depending upon the amount and the kind of alloy。 The low alloy structural steels are sold almost entirely in the form of hot-rolled structural shapes。These materials have good weldability，ductillity，better impact strength than that of plain carbon steel，and good corrosion resistance，particularly to atmospheric exposure。Many building codes are based on the more conservation use of plain carbon steels，and the use of alloy structural steel often has no economic advantage in these cases。LOW ALLOY AISI STEELSImproved Properties at Higher Cost。 The low alloy American Iron and Steel Institute plain carbon steels are alloyed primarily for improved hardenability。They are more costly than plain carbon steels，and their use can generally be justified only when needed in the heat-treat-hardened and tempered condition。Compared to plain carbon steels，they can have 30%40% higher yield strength and 10%20% higher tensile strength。At equivalent tensile strengths and hardnesses，they can have 30%40% higher reduction of area and approximately twice the impact strength。Usually Heat Treated。 The low alloy AISI steels are those containing less than approximately 8% total alloying elements，although most commercially important steels contain less than 5%。The carbon content may vary from very low to very high，but for most steels it is in the medium range that effective heat treatment may be employed for property improvement at minimum costs。The steels are used widely in automobile，machine tool，and aircraft construction，especially for the manufacture of moving parts that are subject to high stress and wear。STAINLESS STEELS Tonnage-wise，the most important of the higher alloy steels are a group of high chromium steels with extremely high corrosion and chemical resistance。Most of these steels have much better mechanical properties at high temperatures。This group was first called stainless steel。With the emphasis on high temperature use，they are frequently referred to as heat and corrosion-resistant steels。Martensitic Stainless Steel。 With lower amounts of chromium or with silicon or aluminium added to some higher chromium steels，the material responds to heat treatment much as any low alloy steal。The gamma-to-alpha transformation in iron occurs normally，and the steel may be hardened by heat treatment similar to that used on plain carbon or low alloy steels。Steel of this class are called martensitic，and the most ones have 4% to 6% chromium。Ferritic Stainless Steel。 With large amounts of chromium， as great as 30% or more，the austenite region of the iron-carbon equilibrium diagram is suppressed，and the steel loses its ability to be hardened by normal steel heat-treating procedures。Steels of this type are called ferritic and are particularly useful when high corrosion resistance is necessary in cold-worked product。Austenitic Stainless Steel。With high chromium and the addition of 8% or more of nickel or combinations of nickel and manganese，the ferrite region of the diagram is suppressed。These steels，the most typical of which contain 18% chromium and 8% nickel，are referred to as austenitic stainless steels。They are not hardenable by normal steel heat-treating procedures，but the addition of small amount
- 温馨提示:
1: 本站所有资源如无特殊说明，都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
2: 本站的文档不包含任何第三方提供的附件图纸等，如果需要附件，请联系上传者。文件的所有权益归上传用户所有。
3.本站RAR压缩包中若带图纸，网页内容里面会有图纸预览，若没有图纸预览就没有图纸。
4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
5. 人人文库网仅提供信息存储空间，仅对用户上传内容的表现方式做保护处理，对用户上传分享的文档内容本身不做任何修改或编辑，并不能对任何下载内容负责。
6. 下载文件中如有侵权或不适当内容，请与我们联系，我们立即纠正。
7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
人人文库网所有资源均是用户自行上传分享，仅供网友学习交流，未经上传用户书面授权，请勿作他用。
川公网安备: 51019002004831号