不銹鋼加工切削常見特點-北京不銹鋼加工廠

    北京圣恩斯特不銹鋼加工廠，提醒大家注意在加工的時候一定要仔細越讀。

    一般鋼材在切削溫度的作用下，切屑切離部位的金屬強度和硬度，將隨切削溫度的升高而明顯下降使切削過程進行順利。不銹鋼在高溫時的強度和硬度無明顯下降，因此不銹鋼加工切削過程的切削力大。切削不銹鋼時，不僅產(chǎn)生的熱量多，而且不銹鋼的導(dǎo)熱率低（約為普通碳素鋼的?~），散熱條件不好，造成刀具高溫，對刀具的壽命有很大的影響。不銹鋼的粘結(jié)凝焊性強，切削過程容易產(chǎn)生積屑瘤，不易獲得光潔的加工表面；不銹鋼的加工硬化傾向強，如切削條件不當(dāng)，刀具磨損加快。不銹鋼切屑不易折斷、卷曲，在切削過程中容易堵塞，造成表面光潔度下降，擠壞加工表面和崩壞刀刃。    不銹鋼由于Cr、Ni含量高，對于以Mn代Ni的不銹鋼，主要是Mn的含量高。正是由于不銹鋼中的Ni（Mn）、Cr含量高于普碳鋼約十倍左右，因此盡管從抗拉強度和屈服極限來說，不銹鋼并不比一般鋼材高多少，甚至不如一般鋼材。不銹鋼的其它性能指標(biāo)，如延伸率、斷面收縮率和沖擊值都比普通碳素鋼及合金鋼高。
    針對不銹鋼加工切削的特點，應(yīng)選用硬度高、抗粘結(jié)性能好、強度高的刀具材料；硬質(zhì)合金刀具應(yīng)選擇含鉭、含鈮的品種，比如YG8；高速鋼刀應(yīng)選擇含鈷的品種；選擇合理的刀具幾何形狀，對低硬度、高塑性的不銹鋼采用較大的前角與后角；采取使切屑卷曲的措施（如卷屑槽等），刀具應(yīng)有足夠的容屑空間務(wù)使切屑卷曲排出流暢；確定合理的切削條件，選用較大的進給量（大于硬化層厚度）和較低的切削速度；切削深度應(yīng)大于前工序留下的硬化層厚度。盡可能提高機床、工件、刀具系統(tǒng)的剛性；選用抗粘結(jié)和散熱性能好的冷卻潤滑液。

1)加工硬化嚴重：在不銹鋼中，以奧氏體和奧氏體+鐵素體不銹鋼的加工硬化現(xiàn)象最為突出。如奧氏體不銹鋼硬化后的強度sb達1470～1960MPa，而且隨sb的提高，屈服極限ss升高；退火狀態(tài)的奧氏體不銹鋼ss不超過的σb30%～45%，而加工硬化后達85%～95%。加工硬化層的深度可達切削深度的1/3或更大；硬化層的硬度比原來的提高1.4～2.2倍。因為不銹鋼的塑性大，塑性變形時品格歪扭，強化系數(shù)很大；且奧氏體不夠穩(wěn)定，在切削應(yīng)力的作用下，部分奧氏體會轉(zhuǎn)變?yōu)轳R氏體；再加上化合物雜質(zhì)在切削熱的作用下，易于分解呈彌散分布，使切削加工時產(chǎn)生硬化層。前一次進給或前一道工序所產(chǎn)生的加工硬化現(xiàn)象嚴重影響后續(xù)工序的順利進行。 

2) 切削力大：不銹鋼在切削過程中塑性變形大，尤其是奧氏體不銹鋼(其伸長率超過45號鋼的1.5倍以上)，使切削力增加。同時，不銹鋼的加工硬化嚴重，熱強度高，進一步增大了切削抗力，切屑的卷曲折斷也比較困難。因此加工不銹鋼的切削力大，如車削1Cr18Ni9Ti的單位切削力為2450MPa，比45號鋼高25%。 

3) 切削溫度高：切削時塑性變形及與刀具間的摩擦都很大，產(chǎn)生的切削熱多；加上不銹鋼的導(dǎo)熱系數(shù)約為45號鋼的?～?，大量切削熱都集中在切削區(qū)和刀—屑接觸的界面上，散熱條件差。在相同的條件下，1Cr18Ni9Ti的切削溫度比45號鋼高200℃左右。 

4) 切屑不易折斷、易粘結(jié)：不銹鋼的塑性、韌性都很大，車加工時切屑連綿不斷，不僅影響操作的順利進行，切屑還會擠傷已加工表面。在高溫、高壓下，不銹鋼與其他金屬的親和性強，易產(chǎn)生粘附現(xiàn)象，并形成積屑瘤，既加劇刀具磨損，又會出現(xiàn)撕扯現(xiàn)象而使已加工表面惡化。含碳量較低的馬氏體不銹鋼的這一特點更為明顯。 

5) 刀具易磨損：切削不銹鋼過程中的親和作用，使刀—屑間產(chǎn)生粘結(jié)、擴散，從而使刀具產(chǎn)生粘結(jié)磨損、擴散磨損，致使刀具前刀面產(chǎn)生月牙洼，切削刃還會形成微小的剝落和缺口；加上不銹鋼中的碳化物(如TiC)微粒硬度很高，切削時直接與刀具接觸、摩擦，擦傷刀具，還有加工硬化現(xiàn)象，均會使刀具磨損加劇。 

6) 線膨脹系數(shù)大：不銹鋼的線膨脹系數(shù)約為碳素鋼的1.5倍，在切削溫度作用下，工件容易產(chǎn)生熱變形，尺寸精度較難控制。

文章來源：（http://www.jaggibuildtech.com） 

Beijing San Ernst stainless steel processing factory, remind everybody attention in processing time must be carefully read.
General steel in the cutting temperature, cutting off the strength and hardness of metal parts, will increase the cutting temperature decreased and the cutting process smoothly. The hardness and strength of the stainless steel at high temperature decreased, so the cutting force of machining process of stainless steel. When cutting stainless steel, not only generate more heat, and so the low thermal conductivity (about ordinary carbon steel ? ~), cooling condition is not good, cause the tool for high temperature, has a great influence on the service life of the cutter. Stainless steel bonded gas welding cutting process is strong, easy to produce the bue, not easy to get the processing surface hardening stainless steel; the strong tendency, such as improper cutting conditions, accelerate tool wear. Stainless steel swarf is not easy to break, crimp, easy to plug in the cutting process, resulting in surface roughness decreased, squeeze bad processing surface and the collapse edge. So since Cr, high Ni content, for Mn generation of Ni stainless steel, the main is the high content of Mn. It is because of stainless steel in the Ni (Mn), the content of Cr was higher than ordinary carbon steel is about ten times, so the tensile strength and the yield limit, stainless steel than the general steel high many, even less than ordinary steel. Other properties of stainless steel, such as elongation, section shrinkage rate and impact value than the ordinary carbon steel and alloy steel.
According to the characteristics of cutting stainless steel processing, should choose the tool material hardness, anti adhesive performance is good, high strength; cemented carbide cutting tools should be selected with a tantalum, niobium containing species, such as YG8; high speed steel should choose the cobalt containing species; selection of tool geometry and reasonable, the low hardness, high plasticity stainless steel using larger front and back angle; take the chip curling measures (such as chip curling groove), the tool should be enough chip space to make chip curling discharged fluently; determine the reasonable selection of cutting conditions, the amount of feed larger (greater than that of the hard layer thickness) and lower cutting speed; cutting depth should be greater than the thickness of hardened layer processes before leaving. As far as possible to improve machine tool, workpiece, cutter system rigidity; select the anti adhesive and good heat dissipation performance of lubricating oil.
1) severe work hardening: in stainless steel, austenite and austenite and ferrite in hardening stainless steel is the most prominent. Such as the strength of sb austenitic stainless steel hardened to 1470 ~ 1960MPa, and with the increase in sb, SS increased the yield limit; annealing of austenitic stainless steel SS does not exceed the σ b30% ～ 45%, whereas the work hardening up to 85% ~ 95%. The depth of hardening layer depth of cut of 1/3 or greater; hardened layer hardness than the original increase 1.4 ~ 2.2 times. Because the stainless steel and plastic, plastic deformation character crooked, enhancement coefficient greatly; and the austenite is not stable enough, the cutting forces, part austenite transforms into martensite; plus compound impurities in cutting under the action of heat, easy to decompose dispersed, so that machining hardening layer. Work hardening phenomenon generated before a feed or a procedure seriously affect the latter procedure
2) cutting force: stainless steel in the process of cutting large plastic deformation, especially in austenitic stainless steel (more than 1.5 times the elongation of 45 steel, the cutting force increase). At the same time, stainless steel hardening, high thermal strength, further increases the cutting force, cutting crimp break is also difficult. So the processing of stainless steel cutting force, such as unit cutting force in turning 1Cr18Ni9Ti into 2450MPa, more than 45 steel high 25%.
3) high cutting temperature: friction and plastic deformation and cutting are great when cutting, the cutting heat generated; and the thermal conductivity of stainless steel is about steel 45 ? to ?, a lot of cutting heat is concentrated at the cutting zone and tool chip contact interface, poor cooling conditions. In the same conditions, 1Cr18Ni9Ti cutting temperature more than 45 steel high 200 ℃.
4) chip is not easy to break, easy bonding: stainless steel plastic, toughness, vehicle processing chips without stop, not only affects the operation smoothly, the chip will squeeze the machined surface. At high temperature and high pressure, stainless steel and other metal affinity strong, easy to produce adhesion phenomena, and the formation of bue, tool wear is intensified, appeared again tear phenomenon at the machined surface deterioration. The characteristics of martensitic stainless steel with low carbon content of the more obvious.
5) the tool wear: affinity cutting stainless steel process, the tool chip produced between the bond, diffusion, so that the tool produces adhesion wear, diffusion wear, crater causing the rake face of the tool, cutting edge but also the formation of tiny flakes and gap; plus stainless steel (such as TiC carbide) particles, high hardness, cutting and cutter contact, friction, abrasion tool, and work hardening phenomenon, can cause the tool wear.
6) linear expansion coefficient: stainless steel linear expansion coefficient is about 1.5 times that of steel, the cutting temperature, the workpiece is easy to produce thermal deformation, dimensional accuracy is difficult to control.
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