High-manganese wear-resistant steel - 1.3401 - X120Mn12
The precursor and inventor who patented in 1882 a new grade with a Manganese content of 12% Mn in an average concentration was Robert Abbott Hadfield - an English metallurgist born in 28.11.1858, in Sheffield, who made a breakthrough in discovering the extraordinary properties of steel - high wear resistance as a result of the hardening of the product during pressure, by adding 1.00-1.25% Manganese to steel with a carbon range of 1:10 ratio.
The newly developed grade has been a great success and is still used in the production of abrasion-resistant components, which has pushed economic growth in many countries, and components made of other wear-resistant steels have been displaced by their faster wear and tear.
Apart from the high content of Carbon and Manganese in the chemical composition itself, Hadfield steel has no more properties of alloying additives except for Silicon itself, which is usually added as standard in other grades. Some equivalents may have a small range of chromium, nickel and copper.
High-manganese steel in Poland has been given the name 11G12, which is not covered by ministerial and state standards and only occurs according to the industry standard BN-68/0631-04, BN-90/0631-03. Its equivalent according to the German DIN standard is - X120Mn12.
Hadfield's steel, as one of the few carbon alloy steels, has an austenitic structure. It acquires its properties only when saturated in water or oil (with smaller details) in a temperature of 1000-1050℃. High-manganese steel products are non-magnetic, but in tempered, poorly heat treated or cold hardened condition the steel exhibits some ferromagnetic properties.
In addition to abrasion resistance, hadfield steel is pressure and impact resistant, but with parts exposed to friction and abrasion without pressure - emerising, the product does not harden, as a result of which the top layer can be subject to abrasion. Referring to the extremely high abrasion resistance, the other side of the medal is the extremely difficult mechanical processing of the material.
To prepare the product for machining, the Hadfield’s steel is deliberately heated to 500℃ with the next rapid cooling in water, which gives the manganese steel a martensitic structure.
In addition to the 11G12 grade itself, the wear-resistant steels also included the extremely inaccessible 55G15 grade according to BN-68/0631-03.
How to machine wear-resistant hadfield steel
12% of high-manganese steel products are mainly machined with silicon carbide SiC grinding wheels with a coarse grain of 16-36 and a semi-hard bond. In the case of cracks, double-sided conical grinding wheels are used for grinding and mounted grinding points for blister grinding. Grinding should be carried out dry, with medium pressure to prevent the material from heating up, which will cause structural changes and weaken the product.
High-speed steels such as SW18 are too weak for any machining of hadfield steels. For this purpose, when selecting low chip processing parameters, high-speed steel according to the old standard HS18-0-1-10, 1.3265 according to DIN/EN can be used. Sintered carbide of grade H20 can be used to make processing easier. The supersaturated state of the material does not remove the possibility of mechanical processing, however, it is severely impeded, and in the cold-hardened and tempered condition at 540-560℃, the processing will be 1-2 hours faster. After treatment, the steel must be saturated. In addition, it should be mentioned - in the case of factory assembly - that steel in tempered condition has a different volume than in supersaturated state. Machining should only be carried out on the best machine tools that do not show vibrations and shocks.
The simplest method of machining the surface of the product is dry grinding with a medium pressure to prevent heating which may cause changes in the structure of the product. This steel can also be cut with an acetylene/oxygen burner for smaller cross-sections, while machining is possible with the use of high speed cobalt steel tools or sintered carbide.
|Approximate values for the coefficient of linear expansion of non-magnetic steels α.106 between 20℃ and the temperature specified below||Approximate thermal conductivity coefficients of non-magnetic steels at different temperatures|
|mm/m/ ℃||Kal/cm.sec. ℃|
With which methods X120Mn12, 1.3401 steel should be cut
Cutting austenitic 11G12 steel with an acetylene/oxygen burner is not more difficult than cutting ordinary carbon steels. The procedure should take into account the possibility of structural changes caused by heating from high flame temperature. In order to cut the material at a proper speed with an even feed and distance between the torch and the surface of the product, it is recommended to carry out with the use of automatic or semi-automatic devices, using the most advantageous cutting parameters adapted to the thickness of the material being cut, i.e. selection of a good oxygen nozzle, husk, gas pressure and oxygen.
Cutting edges, on which it is impossible to avoid stronger scale formation and minor structural changes, should be ground to a depth of 1-2mm. When cutting with a burner it is recommended to use intensive cooling of the cutting area with a water spray in order to prevent structural changes in the area to be cut with the burner.
In X120Mn12 grade materials, holes can also be freely cut with a burner.
Welding and pad welding of steel X120Mn12 - electrodes, additional treatments and notes
As a result of the low durability of the austenitic structure of X120Mn12 and 11G12 high-manganese steel at elevated temperatures, the only method of welding and surfacing that guarantees the lowest heating and residence of the steel at the temperatures of the degradation of austenite is welding and arc pad welding with small diameter electrodes and low current intensity. Selection of the appropriate electrode grade eliminates the risk of deformation of welded joints and the formation of cracks in the welded joint. Electrodes ES18-8, ES18-8-6, ES24-18, and EN400Mn are used for welding.
11G12 does not withstand without compromising its high mechanical properties of slow heating and cooling at around 400-900℃. Long-lasting welding heat leads to the partial disintegration of the austenitic structure and the release of carbides along the grain boundaries not only in the weld or padding weld, but also in the base material, i.e. in the weld zone.
Sheets, forgings and bars of wear-resistant high-manganese steel
The above described high-manganese wear-resistant steels are specified in the Industry Standard BN-68/0631-03, BN-68/0631-04, BN-90/0631-04 and the Standard PN-EN ISO 4957, according to which are supplied:
- Flat products according to EN 10029, EN 10163
- Open die forged products according to EN 10250
- Steel castings according to EN 10349,