Improvement on the turning process of martensitic steel

This text shows you 5 improvements in turning process of martensitic steel

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Because martensitic steel is sufficiently corrosion resistance to atmospheric, water vapor and saline solutions not exceeding 30 ℃, nitric acid, food media, and organic acids of low concentration. Generally, it is widely used to make parts with corrosion resistance and withstand impact load, such as ball valve, etc.

Martensitic steel has high strength, good plasticity, high hardness and poor thermal conductivity. It is easy to deform during processing. In addition, cutting hardening is severe, cutting resistance is high, cutting temperature is high, which easily leads to severe tool wear, increases shutdown time and tool loading time, and reduces production efficiency. We should make appropriate improvements in the selection of martensitic stainless-steel parts. Make the cutting angle of the tool and the cutting fluid.

martensitic stainless steel

Step 1 - Change the hardness of the material by heat treatment

The hardness of martensitic steel decreases to some extent after heat treatment, which has a great influence on turning. After modulation (quenched at 1000-1050 C, air-cooled after returning to 700-800 C and holding for 2-6 h) The martensite is transformed into tempered cable type, resulting in lower hardness, 230~270HBS. This modified material has good comprehensive mechanical properties and cutting performance, and because the matrix of tempered sorbite, ferrite, contains more than 11.7% chromium and has good corrosivity. Therefore, in order to obtain excellent performance of martensitic stainless steel, a reasonable modulation process must be used.

ASTM A743 CG12 pipe

Step 2 - Selection of tool materials

In the processing of stainless steel workpiece, the reasonable choice of cutting tool material is also an important way to improve productivity. The commonly used turning tool materials are generally high-speed steel such as w184cr4v, w6mo5cr4v2ai and other materials. Because its red hardness is not as good as hard metal. Red hardness’ wear resistance is poor, its service life is relatively low. Commonly used hard metal tool materials are: YG6, YG8, YT15, yt30, yw1, yw2 and other materials. In view of the poor machinability of martensitic stainless steel, tungsten cobalt hard metal blades can be selected. Because the toughness, wear resistance, edge wear resistance, adhesion resistance and thermal conductivity of YG are excellent, and the price is cheaper than those of yw1 and yw2. In terms of cost, YG materials are cost-effective.

Step 3 - Determination of tool geometric angle

(1).Selection of front angle γ of turning tool. Generally, when turning martensitic steel, the front angle of the tool is 10 ° ~ 20 °. During processing, because the cutting of stainless steel material is banded and the cutting force is focused on the front face far away from the main cutting edge, the cutting edge is not easy to be damaged, so a larger front angle should be selected.

(2).Selection of turning tool back angle α. The function of turning tool back angle α is mainly to reduce the rub between the main back cutting surface and the machining surface. The larger the back angle, the lower the strength of the cutting edge and the lower the service life. In order to improve the production efficiency and adopt a small back angle, generally α = 5 ° ~ 8 ° is suitable

(3).Selection of the inclination angle λ of turning tool edge. Generally, λ is – 10 ° ~ – 30 °.

(4).The choice of the main deflection angle of the turning tool. к should be selected according to the shape of the work, the processing position and the condition of knife loading.

(5).The surface roughness of cutting-edge R 0.4-0.2 μ M.

(6).On the structure, the external turning tool can use the external inclined arc chip breaking groove, the curl radius of cutting by the tooltip is large, and the curl radius of cutting chips by the outer edge is small, the chip will turn to the machining surface and break. The chip breaking condition is good. For the cutter, the auxiliary deflection angle can be controlled within 1 °. In this way, the chip removal condition can be improved, and the service life of the cutter can be extended.

Step 4 - Reasonable selection of cutting parameters

According to cutting theory, cutting speed V has the greatest influence on cutting temperature and tool durability. The feed rate f is the second.The back cut α is the smallest. The back-cutting amount α is generally based on the blank size of the material, between 0-3mm. The influence of feed rate f on tool durability is not as great as cutting speed, but it will affect chip breaking and chip removal, and scratch the workpiece surface. The surface quality of machining is affected. The size of AA has a direct impact on cutting resistance and cutting temperature, which is directly related to productivity and machining quality, Therefore, when α is large, F should be reduced accordingly. In short, for stainless steel materials, generally low cutting speed and medium feed rate are selected.

Step 5 - Select suitable cutting fluid

According to the processing characteristics of stainless steel, the selection of cutting fluid should have the following characteristics

(1).Good cooling performance. To ensure that a large amount of cutting heat is taken away from the cutting area during the cutting process, so as to reduce the temperature of the workpiece and the tool, so as to improve the service life and machining quality of the tool.

(2).It has a good lubricating effect. Because of the high toughness of stainless steel, it is easy to produce chip accretion when cutting, which worsens the machining surface. It requires that the chip liquid has a high lubricating performance. During machining, it plays a better lubricating role and improves the surface quality.

(3).With good permeability, it can play a good role in wedge, diffusion and internal lubrication for chips that are not easy to be cut off.

The cutting fluid for martensitic steel, such as sulfurized cutting oil, is often selected. It is not only beneficial to reduce friction, deformation, cutting temperature and cold work hardening. It can also improve the surface quality of parts. In the process of remanufacturing, the number of sharpening is greatly reduced, and the production efficiency will be greatly improved. 

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