Introduction

 

      For the equipment of high-speed rolling the important and actual problem is making and upgrading of high-tensile, wear-resistant rollers. The materials providing necessary hardness and strength, hard metals on the basis of a carbide of the titan and the tungsten carbide, gained by a method of hot vacuum pressing are. The important problem is making of wear-resistant rollers with a core from cheaper and during too time of more plastic and viscous material and a hard-alloy surface.

      For multilayered compositions the important problem is the coordination of coefficient of thermal expansion of courses. At inconsistency of thermal expansion at cyclic refrigeration and a heating of products from such materials probably occurrence of flaws and product shattering. The scientific importance of operation consists in an establishment of character of shattering and crack propagation at a temperature cycling, an establishment of coefficients of thermal expansion of builders of a composition, studying of features of structure and properties Butt area.

 

The basic results

 

     Iron-nickel alloys allow to gain a wide gamut of a variation of coefficient of the linear thermal spreading depending on alloy makeup. Hence, it is possible to pick up such makeup of the alloy which linear expansion coefficient will correspond to what linear expansion coefficient or the given material.

      Samples of the composite material consisting of two courses were studied: alloy iron-nickel (45 % Ni) and hard-facing alloys (ÂÊ15 and ÒÆÍ). During explorations photos of microstructures in a band about a butt and in the heart of an alloy have been gained. Trials on a temperature cycling of samples with a heating to 700ºC and refrigeration in water were conducted. Also the sample alloy iron-nickel was exposed to dilatometric trials for the purpose of linear expansion coefficient definition.

      In drawing 1 photomicrographs of a band about a butt (a) and alloy iron-nickel (b) made on not etched samples are shown.

 

 

                           a                                                         b                              

     Picture 1 - Photomicrographs of a band about a butt (a) and alloy iron-nickel (b) made on not etched samples (magnification 50Õ).

 

      From the picture 1 it is possible to score, that in iron-nickel an alloy sites of pluggings of carbides are observed. Exploration of a microhardness of the yielded pluggings has shown, that it coincides with hardness of hard metal. The parent of occurrence of such pluggings completely is not clear. Apparently, their presence is bundled to presence of the rests of hard metal of the trommel which has settled on walls of an attritor and bodies for a milling.

      On the picture 2 the microstructure the alloy iron-nickel, revealed by pickling treatment in a ferric chloride solute is shown.

      

                          a                                                             b

Picture 2 – The Microstructure alloy iron-nickel; – magnification 100Õ (a), - magnification 250Õ (b).

 

      Apparently from a picture 2 in structure presence of the laminar formations reminding an eutecticum or eutectoid is scored. Probably also, that formation of similar structure is bundled to heterogeneity of an alloy and not completely past interdiffusion of builders in a sintering process.

      However, it is necessary to score, that presence of such structures is noted not in all mass of a material, and in some sites. As is shown in a picture 3, in a band about a butt (a) and in separate sites in the heart of an alloy (b) slaty structures it is not revealed.

 

                           a                                                               b

     Picture 3 – The Microstructure alloy iron-nickel; (a)  a band about a butt, (b)  in alloy mass (magnification 250Õ)

 

      From a picture 3 also it is necessary to score essential grain refinement in field about a butt.

      Significant odds in a microhardness of the sites having a slaty structure and sites, having equiaxial structure it is not revealed. But it is possible to guess, that slaty structures have, though and is insignificant, but higher hardness.

      The temperature cycling of samples has shown, that compositions iron-nickel of an alloy with hard metals on the basis of tungsten carbide on a cobaltic sheaf (ÂÊ15) and on the basis of a carbide of the titan on iron-nickel to a sheaf (ÒÆÍ) has various character of shattering. So on the sample consisting from iron-nickel of an alloy and hard metal ÒÆÍ, at the sixth refrigeration there was an appreciable flaw. The flaw has transited on iron-nickel to an alloy to in parallel demarcation apart 0,3 - 0, 45 mm. The sample, from alloy and hard metal ÂÊ15 iron-nickel has appeared much more proof to a temperature cycling as shattering signs in it have occurbed only after the seventeenth refrigeration. In this case the flaw has gone on hard metal to perpendicularly demarcation. It is necessary to score also, that flaw studying under a microscope has shown, that the flaw extremity in a butt band has the T-shaped moulding box.

      Distinction in character of shattering and firmness to a temperature cycling speaks distinction in thermal expansion coefficients, and also various plasticity of alloys ÂÊ15 and ÒÆÍ. So it is possible to score, that the coefficient of thermal expansion of alloy ÂÊ15 is more compounded with coefficient of thermal expansion iron-nickel of an alloy from 45 % of nickel.

      Dilatometric trials have shown alloy iron-nickel, that at temperature nearby 400ºC jump of coefficient of the linear thermal expansion is observed. It shows the diagramme on a picture 4.

         Picture 4 – Elongation of the sample of a double-humped iron-nickel alloy from temperature

                        

 

         Value of coefficient of the linear thermal expansion in the range of temperatures 50 - 400ºC makes 6,829·10^-6 Ê^-1, and in the range of temperatures 450 - 580ºC 14,56·10^-6 Ê^-1. Change of coefficient of the linear thermal expansion is obviously bundled to the magnetic transmutation occurring in an alloy.

          The microhardness of a double-humped iron-nickel alloy in a band between a flaw and hard metal has made 616±29,8 Í/ìì²; at the same time the microhardness in the bulk a double-humped iron-nickel alloy has made 559±15,1 Í/ìì². Hence, the double-humped iron-nickel alloy in a band between a flaw and hard metal has major hardness, that, apparently, is bundled to the diffusive processes which were taking place at pressing and sintering of the sample. It is necessary to mark also that fact, that the microhardness of a double-humped iron-nickel alloy in a band between a flaw and hard metal is not fixed, and is diminished as approaching a flaw as is shown in a picture 5.

     Picture 5 – Dependence of a microhardness on distance on a demarcation.

 

         Apparently from a picture 5, the microhardness practically same, as well as in an original material becomes apart more narrow about 0,2 mm from a demarcation.

 

The inference

 

         From the above-stated follows, that the double-humped iron-nickel alloy containing 45 % of nickel can be successfully used for making of compositions in a combination to hard metal ÂÊ15, but the perspective of its use in a combination to alloys on the basis of a carbide of the titan is much worse looks. Exploration has displayed, that the yielded double-humped iron-nickel alloy has a linear expansion coefficient close to alloy ÂÊ15 in the range of 50 - 400ºC. At the further heat the linear expansion coefficient sharply varies, hence, having heated to temperatures above 400 ºC is extremely undesirable. Refrigeration at manufacture of compositions to 400 ºC should be led in a slowed-up way.